insert text between html tags

string x ="<tr></tr><tr></tr>"
i want to insert some text before the end of second row </tr>
output should be
string x ="<tr></tr><tr>abc</tr>"
the following insert adds before the end of first closing tag, but i want it before the second closing tag
string x = x.insert(x.indexof("</tr>"), "abc");
 
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